Counties with the longest streak of voting for one party for President

[Nym90]

Idaho

D: Blaine (since 1988)
R: Clark (since 1932)

Illinois

D: Alexander, Cook, St. Clair (since 1972)
R: Edwards, Lee, Ogle (I in 1912, never D in the history of the Atlas which goes back to 1892)

Indiana

D: Lake (since 1972)
R: Hamilton, Hendricks (since 1912)

Iowa

D: Dubuque (since 1956)
R: Cass, Page (since 1932)

Kansas

D: Wyandotte (since 1972)
R: Doniphan (never D in Atlas history which goes back to 1888)

Kentucky

D: Elliot (Never R in Atlas history which dates to 1940)
R: Adair, Allen, Butler, Casey, Clay, Clinton, Cumberland, Edmonson, Grayson, Jackson, Laurel, Leslie, Lewis, McCreary, Monroe, Owsley, Pulaski, Rockcastle, Russell (never D in continuous Atlas history which goes back to 1940, although Jackson and McCreary voted I in 1912 and Adair, Allen, Casey, Edmonson, Grayson, Laurel and Pulaski voted D in 1912)

Louisiana

D: East Carroll, Iberville, Madison, Orleans, St. Helena, St. James (since 1972)
R: Bossier, Jefferson, Lafayette, La Salle, Ouachita, St. Tammany, Union (since 1968 when all voted I. Bossier has the longest streak of not voting D, having last went D in 1944)

[Nym90]

Maine

D: Androscoggin, Aroostook, Cumberland, Franklin, Hancock, Kennebec, Knox, Oxford, Sagadohoc, York (since 1988)
R: Piscataquis (since 1996)

Maryland

D: Baltimore City (since 1956), Prince George's (since 1972)
R: Garrett (since 1912 when it voted I, hasn't voted D in Atlas history which dates to 1900)

Massachusetts

D: Suffolk (since 1924)
R: None. The last time any counties went R were Barnstable, Plymouth, and Worcester in 1988.

Michigan

D: Wayne (since 1928)
R: Missaukee, Ottawa, Sanilac (since 1912 when they all voted I, and none have gone D in Atlas history which dates to 1884)

Minnesota

D: Ramsey (since 1924)
R: Carver, Otter Tail (since 1932)

Mississippi

D: Claiborne, Holmes, Jefferson (since 1964)
R: Choctaw, Clarke, Forrest, Franklin, Harrison, Jackson, Jones, Lamar, Lauderdale, Lincoln, Lowndes, Newton, Rankin, Scott, Simpson, Smith, Warren (since 1968 when all voted I, though Clarke was a tie in 1980). Forrest has the longest streak of not voting D, having not done so since 1944.

Missouri

D: St. Louis City (since 1924), Jackson (since 1972)
R: Gasconade, Putnam, Taney (never D in Atlas history which dates to 1888)

Montana

D: Deer Lodge (since 1924)
R: Beaverhead, Fallon, Powder River, Stillwater, Sweet Grass (since 1936)

[Nym90]

Nebraska

D: Thurston (since 2000)
R: Keya Paha (since 1916)

Nevada

D: Clark (since 1988)
R: Douglas (since 1936)

New Hampshire

D: Cheshire, Grafton, Merrimack, Strafford (since 1988)
R: None. The last counties to vote R were Belknap, Carroll, Hillsborough, and Rockingham in 2004.

New Jersey

D: Essex (since 1972)
R: Hunterdon, Morris, Sussex, Warren (since 1964)

New Mexico

D: Rio Arriba, San Miguel (since 1956)
R: Lincoln (since 1936)

New York

D: Bronx, Kings, New York (since 1924). Outside of NYC it would be Albany and Erie, both since 1972.
R: Allegany, Genesee, Greene, Hamilton, Livingston, Orleans, Putnam, Steuben, Tioga, Wayne, Wyoming (since 1964)

North Carolina

D: Northampton (Never R in Atlas history which dates to 1924)
R: Avery, Mitchell, Wilkes, Yadkin (Never D in Atlas history dating to 1924, though Avery, Mitchell, and Wilkes voted I in 1912)

North Dakota

D: Rolette (since 1952)
R: Golden Valley, Grant, Kidder, Logan, McIntosh, Mercer, Sheridan (since 1936)

Ohio

D: Belmont, Cuyahoga, Jefferson, Mahoning, Monroe, Trumbull (since 1972)
R: Delaware (since 1916)

Oklahoma

D: None (Cherokee, Choctaw, Haskell, Hughes, Latimer, McIntosh, Muskogee, Okmulgee, Ottawa all voted D in 2000, the last time any county voted D)
R: Major (since 1932)

Oregon

D: Columbia (since 1928)
R: Josephine (since 1936)

Pennsylvania

D: Philadelphia (since 1932)
R: Snyder, Union, Wayne (since 1912 when all voted I, Snyder and Union haven't voted D in Atlas history which dates to 1888)

Rhode Island

D: Providence (since 1972)
R: None (Bristol, Kent, Newport, and Washington voted R in 1984, the last time any county voted R)

[Nym90]

South Carolina

D: Allendale, Clarendon, Fairfield, Hampton, Jasper, Lee, McCormick, Marion, Marlboro, Orangeburg, Williamsburg (since 1972)
R: Aiken (since 1952)

South Dakota

D: Shannon (since 1952)
R: Lawrence (since 1916)

Tennessee

D: Jackson (since 1920)
R: Cocke, Hancock, Wayne (Never D in Atlas history which dates to 1912)

Texas

D: Brooks, Duval, Jim Hogg, Maverick, Starr, Webb, Zapata (never R in consecutive Atlas history which dates to 1940, though Webb and Zapata voted R in 1912)
R: Kendall (Never D in Atlas history which dates to 1940, though it voted I in 1912)

Utah

D: Grand, Salt Lake, Summit (since 2004)
R: Garfield, Iron, Kane, San Juan, Sanpete, Sevier (since at least 1936 for which no data exists, Garfield, Iron, Kane, and San Juan otherwise have the longest streak having voted R since 1916)

Vermont

D: Addison, Chittenden, Franklin, Grand Isle, Windham (since 1984)
R: None. The last to vote R was Essex in 2004.

Virginia

D: Charles City (since 1956)
R: Floyd (never D in Atlas history which dates to 1932, though it voted I in 1912)

Washington

D: Grays Harbor (since 1928)
R: Adams (since 1936)

West Virginia

D: Boone, Braxton, Marion, McDowell, Webster (since 1972)
R: Morgan (never in Atlas history which dates to 1912)

Wisconsin

D: Douglas (since 1928)
R: Walworth (since 1912).

Wyoming

D: Teton (since 2000)
R: Crook, Johnson (since 1932)

[minionofmidas]

Hmm. So maybe it's really the 1964 results that are surprising there. Perhaps blacks were allowed to vote a little earlier here than in the Deep South?

Quite plausible.

EDIT: (from some letter on the internet)
"I'd like to share my own impression of John Salter, whom I first saw on a 1963 television newscast being mercilessly pummeled by a group of white men.  The attack took place during a Black student demonstration in Jackson, Mississippi [Salter is white and Arizonan. L.T.]  A few months later, John appeared in my rural, eastern North Carolina community, where we Black people were staging our own demonstrations.

(...) Salter's civil rights record, his obvious sincerity, as well as his willingness to take on the local racists, soon won over the most skeptical among us.  For over a year, he worked in our community, facing daily death threats, abuse, and the virulent hatred of local white people.

With John Salter's help, we initiated a countywide voter registration drive, and when local officials set up obstacles, John convinced a battery of topnotch lawyers to challenge the county board of elections in court.  Our side won.   For the first time since the disenfranchisement of Blacks in the late nineteenth century, thousands of eastern North Carolina Blacks registered. (...)"

[Nym90]

Hmm. So maybe it's really the 1964 results that are surprising there. Perhaps blacks were allowed to vote a little earlier here than in the Deep South?

Quite plausible.

EDIT: (from some letter on the internet)
"I'd like to share my own impression of John Salter, whom I first saw on a 1963 television newscast being mercilessly pummeled by a group of white men.  The attack took place during a Black student demonstration in Jackson, Mississippi [Salter is white and Arizonan. L.T.]  A few months later, John appeared in my rural, eastern North Carolina community, where we Black people were staging our own demonstrations.

(...) Salter's civil rights record, his obvious sincerity, as well as his willingness to take on the local racists, soon won over the most skeptical among us.  For over a year, he worked in our community, facing daily death threats, abuse, and the virulent hatred of local white people.

With John Salter's help, we initiated a countywide voter registration drive, and when local officials set up obstacles, John convinced a battery of topnotch lawyers to challenge the county board of elections in court.  Our side won.   For the first time since the disenfranchisement of Blacks in the late nineteenth century, thousands of eastern North Carolina Blacks registered. (...)"

Fascinating stuff! Thanks.

It's just amazing to me that this one county only has managed to vote continuously Democratic, the last remaining remant of the old Solid South (well unless you consider South Texas part of the South).

[RI]

Idaho

D: Blaine (since 1988)
R: Clark (since 1932)

Illinois

D: Alexander, Cook, St. Clair (since 1972)
R: Edwards, Lee, Ogle (I in 1912, never D in the history of the Atlas which goes back to 1892)

Indiana

D: Lake (since 1972)
R: Hamilton, Hendricks (since 1912)

Iowa

D: Dubuque (since 1956)
R: Cass, Page (since 1932)

Kansas

D: Wyandotte (since 1972)
R: Doniphan (never D in Atlas history which goes back to 1888)

Kentucky

D: Elliot (Never R in Atlas history which dates to 1940)
R: Adair, Allen, Butler, Casey, Clay, Clinton, Cumberland, Edmonson, Grayson, Jackson, Laurel, Leslie, Lewis, McCreary, Monroe, Owsley, Pulaski, Rockcastle, Russell (never D in continuous Atlas history which goes back to 1940, although Jackson and McCreary voted I in 1912 and Adair, Allen, Casey, Edmonson, Grayson, Laurel and Pulaski voted D in 1912)

Louisiana

D: East Carroll, Iberville, Madison, Orleans, St. Helena, St. James (since 1972)
R: Bossier, Jefferson, Lafayette, La Salle, Ouachita, St. Tammany, Union (since 1968 when all voted I. Bossier has the longest streak of not voting D, having last went D in 1944)

Doniphan County, KS definitely never voted Democratic.

Lee County, IL voted Democratic in 1852. Edwards County voted Whig last in 1856 (Never D, though). Ogle County voted Whig last in 1852 (Never D, though).

Elliott County, KY never voted Republican, though the area it occupies did last in 1868.

Maine

D: Androscoggin, Aroostook, Cumberland, Franklin, Hancock, Kennebec, Knox, Oxford, Sagadohoc, York (since 1988)
R: Piscataquis (since 1996)

Maryland

D: Baltimore City (since 1956), Prince George's (since 1972)
R: Garrett (since 1912 when it voted I, hasn't voted D in Atlas history which dates to 1900)

Massachusetts

D: Suffolk (since 1924)
R: None. The last time any counties went R were Barnstable, Plymouth, and Worcester in 1988.

Michigan

D: Wayne (since 1928)
R: Missaukee, Ottawa, Sanilac (since 1912 when they all voted I, and none have gone D in Atlas history which dates to 1884)

Minnesota

D: Ramsey (since 1924)
R: Carver, Otter Tail (since 1932)

Mississippi

D: Claiborne, Holmes, Jefferson (since 1964)
R: Choctaw, Clarke, Forrest, Franklin, Harrison, Jackson, Jones, Lamar, Lauderdale, Lincoln, Lowndes, Newton, Rankin, Scott, Simpson, Smith, Warren (since 1968 when all voted I, though Clarke was a tie in 1980). Forrest has the longest streak of not voting D, having not done so since 1944.

Missouri

D: St. Louis City (since 1924), Jackson (since 1972)
R: Gasconade, Putnam, Taney (never D in Atlas history which dates to 1888)

Montana

D: Deer Lodge (since 1924)
R: Beaverhead, Fallon, Powder River, Stillwater, Sweet Grass (since 1936)

Garrett County, MD voted D in 1892.

Missaukee County, MI has never voted D. Ottawa County, MI voted D in 1864. Salinac County, MI voted D in 1852.

Gasconade County, MO voted D in 1856. Putnam County, MO voted D in 1860. Taney County, MO voted SD in 1860.

Nebraska

D: Thurston (since 2000)
R: Keya Paha (since 1916)

Nevada

D: Clark (since 1988)
R: Douglas (since 1936)

New Hampshire

D: Cheshire, Grafton, Merrimack, Strafford (since 1988)
R: None. The last counties to vote R were Belknap, Carroll, Hillsborough, and Rockingham in 2004.

New Jersey

D: Essex (since 1972)
R: Hunterdon, Morris, Sussex, Warren (since 1964)

New Mexico

D: Rio Arriba, San Miguel (since 1956)
R: Lincoln (since 1936)

New York

D: Bronx, Kings, New York (since 1924). Outside of NYC it would be Albany and Erie, both since 1972.
R: Allegany, Genesee, Greene, Hamilton, Livingston, Orleans, Putnam, Steuben, Tioga, Wayne, Wyoming (since 1964)

North Carolina

D: Northampton (Never R in Atlas history which dates to 1924)
R: Avery, Mitchell, Wilkes, Yadkin (Never D in Atlas history dating to 1924, though Avery, Mitchell, and Wilkes voted I in 1912)

North Dakota

D: Rolette (since 1952)
R: Golden Valley, Grant, Kidder, Logan, McIntosh, Mercer, Sheridan (since 1936)

Ohio

D: Belmont, Cuyahoga, Jefferson, Mahoning, Monroe, Trumbull (since 1972)
R: Delaware (since 1916)

Oklahoma

D: None (Cherokee, Choctaw, Haskell, Hughes, Latimer, McIntosh, Muskogee, Okmulgee, Ottawa all voted D in 2000, the last time any county voted D)
R: Major (since 1932)

Oregon

D: Columbia (since 1928)
R: Josephine (since 1936)

Pennsylvania

D: Philadelphia (since 1932)
R: Snyder, Union, Wayne (since 1912 when all voted I, Snyder and Union haven't voted D in Atlas history which dates to 1888)

Rhode Island

D: Providence (since 1972)
R: None (Bristol, Kent, Newport, and Washington voted R in 1984, the last time any county voted R)

Northampton County, NC last voted R in 1896. Yadkin County voted CU in 1860, D in 1856.

[nightkey]

Updated for 2008:


Colorado

D: Costilla (since 1924)
R: Elbert (since 1932)

According to the map at geoelections.free.fr/USA/elec_comtes/1924.htm , Costilla County Colorado went Republican in 1924, but they did go Democratic in 1928.

geoelections.free.fr/USA/elec_comtes/1928.htm

[nclib]

Updated for 2008:


Colorado

D: Costilla (since 1924)
R: Elbert (since 1932)

According to the map at geoelections.free.fr/USA/elec_comtes/1924.htm , Costilla County Colorado went Republican in 1924, but they did go Democratic in 1928.

geoelections.free.fr/USA/elec_comtes/1928.htm

Judging by the rest of this thread, by a county voting Democratic "since 1924", he means that such county has voted Democratic every election after 1924, but did not vote Democratic in 1924.

[Nym90]

Yes, that's correct Nclib.

[Nym90]

Updated for 2012:

Alabama

D: Greene, Macon, Sumter (Greene and Sumter voted R in 1964, Macon voted I in 1964, R in 1956)
R: Baldwin, Houston, Lee, Mobile, Shelby (All voted I in 1968, Baldwin, Mobile, and Shelby last voted D in 1952 which is the longest streak of not voting D, though all three voted D/I in 1960, so Houston can make an argument, having last voted D in 1956, but R in 1960).

Arizona

D: Apache (since 1980)
R: Maricopa, Yavapai (since 1948)

Arkansas

D: Chicot, Desha, Jefferson, Lee, Phillips, Woodruff (since 1972)
R: Benton, Sebastian (since 1948)

California

D: Yolo (since 1952)
R: Orange (since 1936)

Colorado

D: Costilla (since 1924)
R: Elbert (since 1932)

Connecticut

D: Hartford (since 1984)
R: Litchfield (since 2008)

Delaware

D: New Castle (since 1988)
R: Sussex (since 1996)

Florida

D: Gadsden (since 1972)
R: Indian River, Lake, Lee, Manatee, Martin, Sarasota (since 1944)

Georgia

D: Baker, Calhoun, Clay, Dooly, Fulton, Hancock, Macon, Quitman, Stewart, Talbot, Taliaferro, Twiggs, Warren (since 1972)
R: Catoosa, Cobb, Columbia, Dade, Fannin, Fayette, Gwinnett, Lee, Lowndes, Walker (since 1976)

Hawaii

D: Hawaii, Honolulu, Kauai, Maui (since 1984)
R: None (Hawaii, Honolulu, Kauai, and Maui all voted R in 1984, the last time any county voted R)

[Nym90]

Idaho

D: Blaine (since 1988)
R: Clark (since 1932)

Illinois

D: Alexander, Cook, St. Clair (since 1972)
R: Edwards, Lee, Ogle (I in 1912, never D in the history of the Atlas which goes back to 1892)

Indiana

D: Lake (since 1972)
R: Hamilton, Hendricks (since 1912)

Iowa

D: Dubuque (since 1956)
R: Cass, Page (since 1932)

Kansas

D: Wyandotte (since 1972)
R: Doniphan (never D in Atlas history which goes back to 1888)

Kentucky

D: Elliott (Never R in Atlas history which dates to 1940)
R: Adair, Allen, Butler, Casey, Clay, Clinton, Cumberland, Edmonson, Grayson, Jackson, Laurel, Leslie, Lewis, McCreary, Monroe, Owsley, Pulaski, Rockcastle, Russell (never D in continuous Atlas history which goes back to 1940, although Jackson and McCreary voted I in 1912 and Adair, Allen, Casey, Edmonson, Grayson, Laurel and Pulaski voted D in 1912)

Louisiana

D: East Carroll, Iberville, Madison, Orleans, St. Helena, St. James (since 1972)
R: Bossier, Jefferson, Lafayette, La Salle, Ouachita, St. Tammany, Union (since 1968 when all voted I. Bossier has the longest streak of not voting D, having last went D in 1944)

[Nym90]

Maine

D: Androscoggin, Aroostook, Cumberland, Franklin, Hancock, Kennebec, Knox, Oxford, Sagadohoc, York (since 1988)
R: Piscataquis (since 1996)

Maryland

D: Baltimore City (since 1956), Prince George's (since 1972)
R: Garrett (since 1912 when it voted I, hasn't voted D in Atlas history which dates to 1900)

Massachusetts

D: Suffolk (since 1924)
R: None. The last time any counties went R were Barnstable, Plymouth, and Worcester in 1988.

Michigan

D: Wayne (since 1928)
R: Missaukee, Ottawa, Sanilac (since 1912 when they all voted I, and none have gone D in Atlas history which dates to 1884)

Minnesota

D: Ramsey (since 1924)
R: Carver, Otter Tail (since 1932)

Mississippi

D: Claiborne, Holmes, Jefferson (since 1964)
R: Choctaw, Clarke, Forrest, Franklin, Harrison, Jackson, Jones, Lamar, Lauderdale, Lincoln, Lowndes, Newton, Rankin, Scott, Simpson, Smith (since 1968 when all voted I, though Clarke was a tie in 1980). Forrest has the longest streak of not voting D, having not done so since 1944.

Missouri

D: St. Louis City (since 1924), Jackson (since 1972)
R: Gasconade, Putnam, Taney (never D in Atlas history which dates to 1888)

Montana

D: Deer Lodge (since 1924)
R: Beaverhead, Fallon, Powder River, Stillwater, Sweet Grass (since 1936)

[Nym90]

Nebraska

D: Thurston (since 2000)
R: Keya Paha (since 1916)

Nevada

D: Clark (since 1988)
R: Douglas (since 1936)

New Hampshire

D: Cheshire, Grafton, Merrimack, Strafford (since 1988)
R: Belknap, Carroll, Rockingham (since 2008)

New Jersey

D: Essex (since 1972)
R: Hunterdon, Morris, Sussex, Warren (since 1964)

New Mexico

D: Rio Arriba, San Miguel (since 1956)
R: Lincoln (since 1936)

New York

D: Bronx, Kings, New York (since 1924). Outside of NYC it would be Albany and Erie, both since 1972.
R: Allegany, Genesee, Greene, Hamilton, Livingston, Orleans, Putnam, Steuben, Tioga, Wayne, Wyoming (since 1964)

North Carolina

D: Northampton (Never R in Atlas history which dates to 1924)
R: Avery, Mitchell, Wilkes, Yadkin (Never D in Atlas history dating to 1924, though Avery, Mitchell, and Wilkes voted I in 1912)

North Dakota

D: Rolette (since 1952)
R: Golden Valley, Grant, Kidder, Logan, McIntosh, Mercer, Sheridan (since 1936)

Ohio

D: Cuyahoga, Mahoning, Trumbull (since 1972)
R: Delaware (since 1916)

Oklahoma

D: None (Cherokee, Choctaw, Haskell, Hughes, Latimer, McIntosh, Muskogee, Okmulgee, Ottawa all voted D in 2000, the last time any county voted D)
R: Major (since 1932)

Oregon

D: Columbia (since 1928)
R: Josephine (since 1936)

Pennsylvania

D: Philadelphia (since 1932)
R: Snyder, Union, Wayne (since 1912 when all voted I, Snyder and Union haven't voted D in Atlas history which dates to 1888)

Rhode Island

D: Providence (since 1972)
R: None (Bristol, Kent, Newport, and Washington voted R in 1984, the last time any county voted R)

[Nym90]

South Carolina

D: Allendale, Clarendon, Fairfield, Hampton, Jasper, Lee, McCormick, Marion, Marlboro, Orangeburg, Williamsburg (since 1972)
R: Aiken (since 1952)

South Dakota

D: Shannon (since 1952)
R: Lawrence (since 1916)

Tennessee

D: Haywood (since 1972)
R: Cocke, Hancock, Wayne (Never D in Atlas history which dates to 1912)

Texas

D: Brooks, Duval, Jim Hogg, Maverick, Starr, Webb, Zapata (never R in consecutive Atlas history which dates to 1940, though Webb and Zapata voted R in 1912)
R: Kendall (Never D in Atlas history which dates to 1940, though it voted I in 1912)

Utah

D: None. Grand, Salt Lake and Summit were the last to vote D in 2008.
R: Garfield, Iron, Kane, San Juan, Sanpete, Sevier (since at least 1936 for which no data exists, Garfield, Iron, Kane, and San Juan otherwise have the longest streak having voted R since 1916)

Vermont

D: Addison, Chittenden, Franklin, Grand Isle, Windham (since 1984)
R: None. The last to vote R was Essex in 2004.

Virginia

D: Charles City (since 1956)
R: Floyd (never D in Atlas history which dates to 1932, though it voted I in 1912)

Washington

D: Grays Harbor (since 1928)
R: Adams (since 1936)

West Virginia

D: None. Boone, Braxton, Jefferson, Marion, McDowell, Monongalia and Webster were the last to vote D in 2008.
R: Morgan (never in Atlas history which dates to 1912)

Wisconsin

D: Douglas (since 1928)
R: Walworth (since 1912).

Wyoming

D: Teton (since 2000)
R: Crook, Johnson (since 1932)

[Nym90]

Updated for 2016:

Alabama

D: Greene, Macon, Sumter (Greene and Sumter voted R in 1964, Macon voted I in 1964, R in 1956)
R: Baldwin, Houston, Lee, Mobile, Shelby (All voted I in 1968, Baldwin, Mobile, and Shelby last voted D in 1952 which is the longest streak of not voting D, though all three voted D/I in 1960, so Houston can make an argument, having last voted D in 1956, but R in 1960).

Arizona

D: Apache (since 1980)
R: Maricopa, Yavapai (since 1948)

Arkansas

D: Chicot, Desha, Jefferson, Lee, Phillips (since 1972)
R: Benton, Sebastian (since 1948)

California

D: Yolo (since 1952)
R: Sutter (since 1940)

Colorado

D: Costilla (since 1924)
R: Elbert (since 1932)

Connecticut

D: Hartford (since 1984)
R: Litchfield (since 2008)

Delaware

D: New Castle (since 1988)
R: Sussex (since 1996)

Florida

D: Gadsden (since 1972)
R: Indian River, Lake, Lee, Manatee, Martin, Sarasota (since 1944)

Georgia

D: Calhoun, Clay, Fulton, Hancock, Macon, Stewart, Talbot, Taliaferro, Warren (since 1972)
R: Catoosa, Columbia, Dade, Fannin, Fayette, Lee, Lowndes, Walker (since 1976)

Hawaii

D: Hawaii, Honolulu, Kauai, Maui (since 1984)
R: None (Hawaii, Honolulu, Kauai, and Maui all voted R in 1984, the last time any county voted R)

[Nym90]

Idaho

D: Blaine (since 1988)
R: Clark (since 1932)

Illinois

D: Cook, St. Clair (since 1972)
R: Edwards, Lee, Ogle (I in 1912, never D in the history of the Atlas which goes back to 1892)

Indiana

D: Lake (since 1972)
R: Hamilton, Hendricks (since 1912)

Iowa

D: Johnson (since 1960)
R: Cass, Page (since 1932)

Kansas

D: Wyandotte (since 1972)
R: Doniphan (never D in Atlas history which goes back to 1888)

Kentucky

D: Jefferson (since 1988)
R: Adair, Allen, Butler, Casey, Clay, Clinton, Cumberland, Edmonson, Grayson, Jackson, Laurel, Leslie, Lewis, McCreary, Monroe, Owsley, Pulaski, Rockcastle, Russell (never D in continuous Atlas history which goes back to 1940, although Jackson and McCreary voted I in 1912 and Adair, Allen, Casey, Edmonson, Grayson, Laurel and Pulaski voted D in 1912)

Louisiana

D: East Carroll, Iberville, Madison, Orleans, St. Helena, St. James (since 1972)
R: Bossier, Jefferson, Lafayette, La Salle, Ouachita, St. Tammany, Union (since 1968 when all voted I. Bossier has the longest streak of not voting D, having last went D in 1944)

[Nym90]

Maine

D: Cumberland, Hancock, Knox, Sagadohoc, York (since 1988)
R: Piscataquis (since 1996)

Maryland

D: Baltimore City (since 1956). Among counties the longest streak is Prince George's (since 1972)
R: Garrett (since 1912 when it voted I, hasn't voted D in Atlas history which dates to 1900)

Massachusetts

D: Suffolk (since 1924)
R: None. The last time any counties went R were Barnstable, Plymouth, and Worcester in 1988.

Michigan

D: Wayne (since 1928)
R: Missaukee, Ottawa, Sanilac (since 1912 when they all voted I, and none have gone D in Atlas history which dates to 1884)

Minnesota

D: Ramsey (since 1924)
R: Carver, Otter Tail (since 1932)

Mississippi

D: Claiborne, Holmes, Jefferson (since 1964)
R: Choctaw, Clarke, Forrest, Franklin, Harrison, Jackson, Jones, Lamar, Lauderdale, Lincoln, Lowndes, Newton, Rankin, Scott, Simpson, Smith (since 1968 when all voted I, though Clarke was a tie in 1980). Forrest has the longest streak of not voting D, having not done so since 1944.

Missouri

D: St. Louis City (since 1924). Among counties the longest streak is Jackson (since 1972)
R: Gasconade, Putnam, Taney (never D in Atlas history which dates to 1888)

Montana

D: Deer Lodge (since 1924)
R: Beaverhead, Fallon, Powder River, Stillwater, Sweet Grass (since 1936)

[Nym90]

Nebraska

D: Douglas, Lancaster (since 2012)
R: Keya Paha (since 1916)

Nevada

D: Clark (since 1988)
R: Douglas (since 1936)

New Hampshire

D: Cheshire, Grafton, Merrimack, Strafford (since 1988)
R: Belknap, Carroll, Rockingham (since 2008)

New Jersey

D: Essex (since 1972)
R: Hunterdon, Morris, Sussex, Warren (since 1964)

New Mexico

D: Rio Arriba, San Miguel (since 1956)
R: Lincoln (since 1936)

New York

D: Bronx, Kings, New York (since 1924). Outside of NYC it would be Albany and Erie, both since 1972.
R: Allegany, Genesee, Greene, Hamilton, Livingston, Orleans, Putnam, Steuben, Tioga, Wayne, Wyoming (since 1964)

North Carolina

D: Northampton (Never R in Atlas history which dates to 1924)
R: Avery, Mitchell, Wilkes, Yadkin (Never D in Atlas history dating to 1924, though Avery, Mitchell, and Wilkes voted I in 1912)

North Dakota

D: Rolette (since 1952)
R: Golden Valley, Grant, Kidder, Logan, McIntosh, Mercer, Sheridan (since 1936)

Ohio

D: Cuyahoga, Mahoning (since 1972)
R: Delaware (since 1916)

Oklahoma

D: None (Cherokee, Choctaw, Haskell, Hughes, Latimer, McIntosh, Muskogee, Okmulgee, Ottawa all voted D in 2000, the last time any county voted D)
R: Major (since 1932)

Oregon

D: Clatsop (since 1956)
R: Josephine (since 1936)

Pennsylvania

D: Philadelphia (since 1932)
R: Snyder, Union, Wayne (since 1912 when all voted I, Snyder and Union haven't voted D in Atlas history which dates to 1888)

Rhode Island

D: Providence (since 1972)
R: Kent (since 2012)

[Nym90]

South Carolina

D: Allendale, Clarendon, Fairfield, Hampton, Jasper, Lee, Marion, Marlboro, Orangeburg, Williamsburg (since 1972)
R: Aiken (since 1952)

South Dakota

D: Oglala Lakota (since 1952)
R: Lawrence (since 1916)

Tennessee

D: Haywood (since 1972)
R: Cocke, Hancock, Wayne (Never D in Atlas history which dates to 1912)

Texas

D: Brooks, Duval, Jim Hogg, Maverick, Starr, Webb, Zapata (never R in consecutive Atlas history which dates to 1940, though Webb and Zapata voted R in 1912)
R: Kendall (Never D in Atlas history which dates to 1940, though it voted I in 1912)

Utah

D: Salt Lake, Summit (since 2012)
R: Kane (since 1916)

Vermont

D: Addison, Chittenden, Franklin, Grand Isle, Windham (since 1984)
R: Essex (since 2012)

Virginia

D: Charles City (since 1956)
R: Floyd (never D in Atlas history which dates to 1932, though it voted I in 1912)

Washington

D: Jefferson (since 1980)
R: Adams (since 1936)

West Virginia

D: None. Boone, Braxton, Jefferson, Marion, McDowell, Monongalia and Webster were the last to vote D in 2008.
R: Morgan (never in Atlas history which dates to 1912)

Wisconsin

D: Douglas (since 1928)
R: Walworth (since 1912).

Wyoming

D: Teton (since 2000)
R: Crook, Johnson (since 1932)

[Bleeding heart conservative, HTMLdon]

Tennessee

D: Haywood (since 1972)
R: Cocke, Hancock, Wayne (Never D in Atlas history which dates to 1912)

According to the maps on the Wikipedia pages for each election, Wayne has been R since 1876.  Cocke and Hancock have been R since 1868.  Hancock did vote for Breckenridge in 1860 but the last time Cocke voted Democrat was for Andrew Jackson in 1832, and even that appears to be by a close margin.

[Nym90]

Tennessee

D: Haywood (since 1972)
R: Cocke, Hancock, Wayne (Never D in Atlas history which dates to 1912)

According to the maps on the Wikipedia pages for each election, Wayne has been R since 1876.  Cocke and Hancock have been R since 1868.  Hancock did vote for Breckenridge in 1860 but the last time Cocke voted Democrat was for Andrew Jackson in 1832, and even that appears to be by a close margin.

Thanks Don. I've stuck to using official Atlas data for this thread (though I jumped the gun a bit this year and used the AP for county results Dave doesn't have posted yet).

[Young Conservative]

My entire congressional district has voted Republican for president since before 1970.

[GMantis]

Based on this list and this series of maps, some additions to Nym's list (not including those counties already mentioned by other users):

Kentucky

R: Clay, Owsley (Since 1860, though both of these counties were substantially bigger at the time

Texas

D: Brooks (Since 1908, ie every time since the county was founded in 1911)

West Virginia:

R: Morgan (Since 1860)

[Nym90]

Thanks Gmantis.